DNA in Tooth Yields New Insight Into Ancient Human Cousin

DNA analysis of a single fossilized tooth found in a Siberian cave has given scientists new insight into a recently discovered hominid group, known as the Denisovans.

A new study, published earlier this week in the journal Proceedings of the National Academy of Sciences, represents a key step in scientists’ understanding of the Denisovans, an ancient hominid group that interbred with early modern humans. In 2008, scientists discovered a tiny finger bone and a few teeth in Denisova cave, located in the Altai Mountains in southern Siberia. Two years later, a team of Russian scientists identified the bone and one of the teeth as belonging to members of the same previously unknown human relative; they called the new group the Denisovans (pronounced “De-NEE-soh-vens”) after the cave where the remains were found.

Analysis of the finger bone and tooth showed the specimens to be at least 50,000 years old. The Denisovans’ closest relatives, the scientists found, were the Neanderthals, a hominin species that lived in Europe and western Asia between 300,000 and 40,000 years ago. Despite common origins, they concluded that the Denisovans were almost as genetically distinct from Neanderthals as Neanderthals were from living people. DNA analysis showed that the Denisovans had made their mark on modern humans, contributing some 5 percent of their DNA to the genomes of present-day Melanesians, who live in Papua New Guinea and other Pacific islands, and around 0.2 percent to the genomes of Native Americans and mainland Asians.

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Because there were so few known Denisovan remains, however, scientists have been limited in what they could determine about the group, which they have not yet definitively called a species. The new study focuses on analysis of a second tooth, uncovered deep in the back of the Denisova cave in 2010. Researchers found that the new tooth, dubbed Denisova 8, bore striking similarities to the previously analyzed Denisovan tooth, while both were significantly different from the teeth of Neanderthals and modern humans. Both teeth were large, with sizeable roots, indicating that their owners must have had very large jaws. In addition, the new tooth showed only half the amount of genetic mutations as the other tooth and the finger bone. Using this evidence, geneticists concluded that the tooth was around 110,000 years old, as many as 60,000 years older than the other two specimens.

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DNA analysis of the new tooth, combined with that of the earlier tooth and finger bone, revealed that the three specimens belong to three different individuals, all Denisovians. As a result, the scientists were able to examine genetic variation among Denisovians for the first time. Although all three remains were found in a single cave, they marveled, the Denisovans appeared to have almost as much genetic diversity as modern Europeans, and were far more genetically diverse than Neanderthals. This conclusion suggests that Denisovans either lived near the cave between 110,000 and 50,000 years ago, or that they came into the region at least twice—either way, the group appears to have been much larger, and to have flourished for much longer, than previously believed.